(1) Field of the Invention
This invention relates to low noise amplifier for wireless communication, in particular to the power consumption of the amplifier.
(2) Description of the Related Art
In mobile wireless communication system, power consumption is an important consideration. The low noise amplifier (LNA) is a major source of power gouging. It is desirable to operate the LNA at low current to conserve power. However, in the presence of jamming the LNA must have a large dynamic range and low intermodulation distortion. To meet these requirements, the LNA must operate at a high enough dc operating current. Thus, the design is often a balance between dynamic range and power consumption.
In a paper by Wei Xiong and Lawrence E. Larson "An S-band Low Noise Amplifier with Self-Adjusting Bias for Improved Power Consumption and Dynamic Range in a Mobile Environment", IEEE Radio Frequency Integrated Circuits Symposium, 1999, it was disclosed to use a power detector to actively control the drain-source current of two cascaded GaAs FET amplifier of the LNA. The control circuit uses an average detector to detect the power level with respect to a fixed reference level. Such a detector detects the average magnitude of the jamming signal rather then the peak value of the jamming signal, whereas the LNA should be designed to accommodate the peak jamming signal rather than the average jamming signal. The fixed reference level may cause the LNA to operate at high current level in the presence of high desired signal. Furthermore, the Wei-Larson circuit was not integrated and there was significant parasitic element losses through the package device lead frame, printed circuit board traces, especially at high frequencies. Their diode and resistors are dissipative elements, as are the resistance voltage divider to derive the reference voltage. Therefore the prior art leaves something to be desired.